The present invention relates to an electromagnet. In particular, the present invention relates to an electromagnet of the type comprising an excitation coil wound as a solenoid and having at least two windings (driving and holding windings) and which can be selectively energised, a core fixedly mounted with respect to the coil, a movable core which can move axially with respect to the coil, a movable core which can move axially with respect to the said coil, and an electric switch which can be actuated by the movable core to supply the windings of the coil selectively.
Electromagnets of the above specified type are widely used, especially in the industrial field, for transmitting displacement commands both in traction and in thrust with forces of the order of units or tens of kilograms. The use of the switch permits the excitation current in the coil to be reduced at the end of the stroke of the movable coil, that is when the electromagnet is in a condition where it only needs to exert a holding force; this arrangement allows, in particular, considerable forces to be obtained in traction or thrust phase whilst eliminating overheating of the coil in that at the end of the stroke the driving winding is put in series with the so-called holding winding by means of the switch and the current is drastically reduced.
For the purpose of making the use of such electromagnets more versatile, the movable core can be provided at the opposite ends with two shafts which conveniently extend out from the body of the electromagnet and which allow this latter to be used both as a thrust electromagnet as well as a pulling electromagnet. Currently there are no commercially available electromagnets provided with switches for division of the electrical supply to the coil and at the same time able to operate in pull and in push mode. In fact only electromagnets which function in pull mode are known, in which the switch is mounted externally and is substantially constituted by a microswitch of the end-of-stroke type, the operating push-button of which is pressed by the movable core of the electromagnet. This microswitch as well as being bulky, is also of low reliability in that being controlled indirectly by the movable core its electrical contacts open and close slowly causing the occurrence of spark phenomena between these latter and a consequent rapid deterioration. Such electromagnets of known type therefore require constant maintenance and do not lend themselves to being equally used as push and pull electromagnets, the microswitch being head mounted above the movable core.